lower chordates PDF

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ZOO 102.1 Comparative Vertebrate Anatomy Laboratory

Name: Ria Ariadne T. Flores

Date conducted: August 15, 2019

Student Number: 2018-09596

Date submitted: August 23, 2019

Exercise no. 1 THE LOWER CHORDATES

In Chordates, there are distinctive characteristics that distinguish them from their ancestors which is the presence of a notochord, a dorsal hollow nerve cord, pharyngeal gill slits, and a muscular post anal tail at some point of their development. The Lower Chordates include the sub-phyla Hemichordata, Urochordata, and Cephalochordata. Subphylum Hemichordata are marine worms which are considered as doubtful chordates exhibited by acorn worms. Subphylum Urochordata are sedentary or planktonic tunicates which are characterized by distinctive characteristics that are not consistently manifested throughout their development. Its representative includes Doliolum. Subphylum Cephalochordata are chordates characterized by the presence of the four distinctive characters throughout their life cycle represented by Amphioxus. This exercise aims to compare and contrast the body plans of various lower chordates. Materials and Methods Prepared slides of Amphioxus male w.m, Amphioxus male c.s, Amphioxus female c.s. and Amphioxus (mature) w.m were examined using the microscope at 10x magnification (low power objective). A slide of Doliolum was also obtained from other sources. Diagrams for each of the specimens were also illustrated and labelled their corresponding parts.

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Results

Photo retrieved from https://planktonnet.awi.de/index.php?contenttype=image_details&itemid=58551#content

Fig. 1. Doliolum at 100x total magnification Figure 1 shows the sagittal view of Doliolum under low power objective of the microscope. At the bottom is the dorsal side.

Fig. 2. Illustration of Doliolum 2

Fig. 3. Amphioxus male w.m. at 100x total magnification Figure 3 shows the whole mount of a male Amphioxus under low power objective of the microscope.

Fig. 4. Illustration of Amphioxus male w.m. 3

Fig. 5. Amphioxus male c.s. at 100x total magnification Figure 5 shows the cross section of a male Amphioxus under low power objective of the microscope.

Fig. 6. Illustration of Amphioxus male c.s.

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Fig. 7. Amphioxus female c.s. at 100x total magnification Figure 7 shows the cross section of a female Amphioxus under low power objective of the microscope.

Fig. 8. Illustration of Amphioxus female c.s. 5

Photo retrieved from http://faculty.baruch.cuny.edu/jwahlert/bio1003/chordata.html

Fig. 9. Amphioxus mature w.m.

Fig. 10. Amphioxus mature w.m. 6

Answers to questions: 1. How are these 3 organisms similar and different? The three lower chordate organisms have the presence of notochord, dorsal hollow nerve chord, pharyngal gill slits, and a muscular, post anal tail. The Hemichordates, however, do not posses a true notochord. Urochordates have post anal tail and notochord (extended in the head region) only in larval stage unlike the Cepahlochordates where it possess post-anal tail and notochord (located at the posterior part) throughout their life cycle. Urochordates are hermaphroditic undergoing asexual reproduction and free-swimming during larval stage but become sessile in adult stage while cephalochordates are unisexual, free-swimming and do not undergo asexual reproduction. Both Urochordates and Cephalochordates lack welldeveloped sensory organs. 2. Why is Amphioxus called the "classic chordate"? The cephalochordate amphioxus is the most basal living chordate having ancestral anatomical characters from vertebrate features. Genome sequencing has been conducted that links it in vertebrate genomes to address the evolution of regenerative mechanisms in chordates at the invertebrate–vertebrate transition. 3. How does a tunicate larva compare to an adult tunicate? In larval stage of a tunicate, it is free-swimming and exhibits all chordate characteristics: it has a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail. It eventually attaches to a hard substrate, it loses its tail and ability to move, and its nervous system largely disintegrates which makes it sessile in its adult stage. 4. Why is the Acorn worm not considered an invertebrate worm?

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Adult acorn worms lack post-anal tail but share such chordate characteristics as pharyngeal gill pores, a partially neurulated dorsal cord, and a stomochord, which is similar to a chordate notochord.

Conclusion In this exercise, among the lower chordates, Amphioxus, representing the Subphylum Cephalochordata, possess the four distinctive characters which are the notochord, dorsal hollow nerve chord, pharyngal gill slits, and a muscular, post anal tail throughout their life cycle. Doliolum from Subphylum Urochordata manifests all four in the larval stage but only the pharyngeal gill slits remain as it develops into an adult. Subphylum Hemichordata, represented by acorn worms, possess pharyngeal gill slits and a dorsal nerve cord but lack a true notochord, instead they have a stomochord, which is similar to a chordate notochord. Nevertheless, all are considered chordates since one or more of the distinctive characteristics were manifested in the specimens used.

References Department of Zoology School of Sciences Uttarakhand Open University. Chordata (BSCZO201).

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http://www.uou.ac.in/sites/default/files/slm/BSCZO-201.pdf Escrivà, H., Somorjai, I., Somorjai, R., Fernàndez, J., Vertebrate-like regeneration in the Inv.ertebrate Chordate Amphioxus. PNAS January 10, 2012. Retrieved on August 19, 2019 from https://doi.org/10.1073/pnas.1100045109

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Lakna. Pediaa. Difference Between Urochordata and Cephalochordata. 2018. Retrieved on August 17, 2019 from https://pediaa.com/difference-between-urochordata-andcephalochordata/ New World Encyclopedia contributors. Acorn worm. 2019. Retrieved on August 19, 2019 from

//www.newworldencyclopedia.org/p/index.php?

title=Acorn_worm&oldid=1017679 UCMP. Introduction to the Urochordata. (n.d.). Retrieved on August 19, 2019 from https://ucmp.berkeley.edu/chordata/urochordata.html

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